This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 8 |
| 5 | 20 |
| 6 | 84 |
| 7 | 266 |
| 8 | 1728 |
| 9 | 5400 |
| 10 | 62400 |
| 11 | 105072 |
| 12 | 3831552 |
| 13 | -6751056 |
| 14 | 393519840 |
| 15 | -2647115280 |
| 16 | 63975266304 |
| 17 | -747746339328 |
| 18 | 15068270944512 |
| 19 | -236303000537472 |
| 20 | 4743900735943680 |
| 21 | -88955061630656256 |
| 22 | 1889497707746457600 |
| 23 | -40170338917074339840 |
| 24 | 919697318458416414720 |